1. Field of the Invention
The present invention relates to a leveling system for motor vehicles, and more particularly to a leveling system for supplying a pneumatic pressure to or discharging a pneumatic pressure from pneumatic chambers attached to hydraulic shock absorbers of a vehicle suspension apparatus.
2. Prior Art
Known leveling mechanism for motor vehicles supply a fluid pressure in a system which differs from a shock absorbing system to adjust the vehicle riding height under different driving and parking conditions. Most of the prior leveling mechanisms utilize a hydraulic pressure, and require costly piping, valves and pumps.
A leveling system using a pneumatic pressure is disclosed in U.S. Pat. No. 2,939,723 to W. E. Wisnieski, patented June 7, 1960. According to the disclosed leveling system, the riding height of a vehicle chassis is automatically adjusted in response to changes in the relationship between the vehicle frame and the road wheels, and a manual override control is incorporated to selectively change the vehicle riding height under load and road conditions. Since systems for supplying air are separately provided respectively for automatic and manual controls, lengthy piping and many valves are required which are complex in construction, resulting in an increase in the weight of the motor vehicle. The conventional leveling system includes air springs disposed at the front and rear of the vehicle and leveling valves provided respectively for the air springs. However, with this arrangement, it is not possible with manual control to adjust the vehicle riding height in opposite directions at the front and rear of the vehicle (for example, to raise the front of the vehicle by supplying air to the front air springs and lower the rear of the vehicle by exhausting air from the rear air springs). Air used under pressure for adjusting the riding height of the vehicle is introduced from the atmosphere which contains considerable humidity. The water in the introduced air tends to create rust in the valves and pipes, with the result that the durability of the leveling system will be reduced.